1. Field of the Invention
The present invention relates to a sealed battery and a manufacturing method thereof.
2. Description of Related Art
As for a conventional sealed battery, Japanese Patent Application Publication No. 2009-259701 A (JP 2009-259701 A), for example, describes a battery for the purpose of relaxing a stress to act on a joint portion of a sealing cap (JP 2009-259701 A). The battery described in JP 2009-259701 A includes a housing having an injection hole, and a sealing cap configured to close the injection hole. A peripheral part of the sealing cap is joined to the housing by welding; and a central part of the sealing cap bends from the peripheral part to project outside the housing.
In addition to that, Japanese Patent No. 4811540 describes a sealed battery for the purpose of closing a whole circumference of an opening formed in a battery container under a given welding condition (Japanese Patent No. 4811540).
In the battery described in JP 2009-259701 A, the sealing cap configured to close the injection hole is joined, by welding, to the housing having the injection hole. However, at the time of welding the sealing cap, when gas inside the housing is heated by welding heat and expands, the gas breaks into a welding atmosphere. In this case, blowholes may occur due to a welding portion entrapping the gas inside the housing. The blowhole is such a phenomenon that air bubbles occur inside the welding portion.